Telescopic-arm lifting vehicles are low on vehicle drive energy efficiency, and have a fairly high noise level; whereas future directives will inevitably call for greater attention to low-consumption performance and low noise levels.
U.S. Pat. No. 5,707,202 illustrates a telescopic-arm vehicle comprising a hydraulic pump; an actuator powered by the hydraulic pump to operate the telescopic arm; and an internal combustion engine housed in a side compartment between the two vehicle axles. More specifically, the compartment houses a number of parts, a compressor, a filter, and a hydraulic valve assembly; and the vehicle is normally driven by a hydraulic (hydrostatic) motor controlled by the internal combustion engine at various speeds.
In vehicles of this sort, the internal combustion engine must be run continuously; and, to drive the vehicle, this transfers energy from the internal combustion engine to the hydraulic motor. Vehicles of this sort are normally four-wheel-drives; and, when the hydraulic lifting system is running, energy is transferred from the internal combustion engine to the pump by a mechanical drive, which means the internal combustion engine is run continuously, both to move the vehicle back and forth, and to operate the arm.
Typical drawbacks of vehicles of this sort are the poor energy efficiency of the system as a whole, and the difficulty in running the internal combustion engine at the most energy-efficient speed, on account of its speed normally being controlled by the accelerator pedal.
Moreover, the vehicle produces contaminating emissions in all operating conditions, and has a high noise level at high engine speed.
A hybrid vehicle operating system is described in JP-A-2005133319, in which the internal combustion engine and electric motor are located at the rear, together with the batteries. This configuration is particularly bulky, raises the centre of gravity, and is ill-suited to the stability required of telescopic-arm vehicles, in which the centre of gravity must be kept as low as possible to safeguard against the vehicle tipping over. Moreover, no mention is made of the problems posed in assembling individual components to minimize impact on the layout of telescopic-arm vehicles.
The hybrid operating system described provides for running the internal combustion engine connected to a generator, which powers a battery pack in turn powering an electric vehicle-drive motor.
More specifically, the internal combustion engine and the electric motor are user-controlled directly by a first pedal to control both the internal combustion engine and the electric motor, and by a second pedal to control the electric motor only. This means the user can also control the speed of the internal combustion engine on the basis of the load demanded of the electric motor, at the expense of the energy efficiency of the vehicle as a whole.
Moreover, the vehicle described is an excavator, which, unlike a telescopic-arm vehicle, needs more or at least the same power to operate the shovel as to drive the vehicle.
This seriously affects the size of hybrid excavator battery packs. That is, to run 1 hour with the electric vehicle-drive motor and the shovel powered fully electrically, i.e. with the internal combustion engine off, an excavator as described in JP-A-2005133319 would need battery packs of a few hundred kWh, which would be too bulky and heavy for the excavator.
The excavator described therefore cannot be run fully electrically to simultaneously drive the vehicle and operate the shovel. On the contrary, the internal combustion engine must be run continuously to simultaneously drive the vehicle and run the hydraulic system, which can only be powered electrically when the vehicle is stationary.
The system described in JP-A-2005133319 therefore mainly provides for energy saving by turning the internal combustion engine off when the vehicle is stationary; using battery power and the reversible electric machine to run the hydraulic systems for a short period, with no emissions while the vehicle is stationary, until the batteries run down below a given threshold; and then restarting the internal combustion engine. Nowhere is any mention made of designing the battery pack and distributing power between vehicle drive and the hydraulic systems, to balance and control power demand in different vehicle operating conditions.